Dingtian input push: HTTP Digest auth + auto-config on assign

Secure the device→backend input push, and configure it automatically when the
admin assigns the device (no manual URL/secret entry).

Auth — HTTP Digest (chosen by hardware testing: the device can't push to a
self-signed HTTPS backend, but does Digest correctly; a URL token is sniffable/
logged):
- digest-auth.ts: MD5 qop=auth challenge/verify, single-use nonces (replay
  resistance). Password never crosses the wire.
- push route: Digest + source-IP allowlist; per-device pushUser/pushPassword from
  lane_devices. Still not behind the SPA cookie/CSRF auth (machine call). The
  signed event log remains the real anti-fraud guarantee.

Auto-config on assign:
- setup assign: for push-capable devices, generate Digest creds, call
  configureInputPush to write them + the push URLs to the device, store the creds
  (password not echoed back). net.ts derives the backend IP on the device's
  subnet (BACKEND_HOST_IP override).
- driver configureInputPush sets auth=2 + creds; PushConfig carries the creds.
- removed the earlier URL-token approach.

Two hard-won device-write bugs fixed in the driver:
- configApi now sets an explicit Content-Length — the device silently ignores
  chunked request bodies (Node's default without Content-Length), so every config
  write looked successful ({"status":0}) but did nothing. This was the root cause
  of the session's "writes don't apply" mystery.
- #writeConfig polls until the change is verified, retrying (the device reboots on
  apply; back-to-back writes were lost). The `pass` field caps at 31 chars, so the
  generated password is 24 hex chars.

Verified on hardware: assign auto-configures the device; all 4 inputs then push
with Digest auth, zero failures. wiki/device-input-flow updated.

apps/server/src/server.ts

@@ -44,8 +44,10 @@ export async function buildServer(opts: BuildOptions = {}): Promise<FastifyInsta
   // catalog at first-run. See wiki/concepts/first-run-setup.md.
   await setupRoutes(app, db);
 
-  // Inbound device pushes (e.g. Dingtian Input Link URL → button events).
-  await deviceRoutes(app);
+  // Inbound device pushes (e.g. Dingtian Input Link URL → button events),
+  // guarded by source-IP allowlist + a shared-secret path token, both read from
+  // the device's lane_devices config (written on assign).
+  await deviceRoutes(app, db);
 
   // TODO: entry flow (input event → signed event → print → relay), event-log routes.